Gear pumps have long been used as positive displacement pumps in a variety of applications with considerable success. As is well known, they typically include a housing having an interior chamber defined by parallel, intersecting, cylindrical bores. A spur gear is disposed in each of the bores along with an associated shaft and the gears mesh in the area of intersection of the bores. Bearings are also disposed in the bores to journal the shafts, and in the usual case, have a generally cylindrical exterior configuration with facing and engaging flats immediately adjacent to the point at which the gears mesh.
On one side of such point, the housing is provided with an outlet, while on the other side, the housing is provided with an inlet.
The gears are driven to rotate in such a way that they unmesh adjacent the inlet to pick a fluid and convey the same around the periphery of the bores to the point at where they mesh. The meshing of the gears forces the fluid out of the space between the individual teeth on the respective gears and out of the outlet.
One persistent difficulty results as a consequence of this basic design. The pressure of the fluid being pumped is greater adjacent the outlet than at the inlet during pump operation. As a consequence, the gears and their shafts are side-loaded, that is, subjected to a force that is generally transverse to the rotational axes of the shafts and generally in the direction from the outlet toward the inlet. Other lesser, but nonetheless significant, forces are present as, for example, those resulting from interengagement of the gear teeth during operation.
The pressure differential causes leakage flow from the outlet to the inlet through the interfaces of the various components which lowers the efficiency of the pump during operation. In general, leakage flow is a very small percentage of the total flow and itself may not be a significant problem. However, in many instances, there are substantial variations in the leakage flow from one identically made pump to another. Even more importantly, the depth of mesh of the spur gears may vary substantially in obtensibly identical pumps. Since the volume pumped is a direct function of the volume displaced by the meshing gears, variation in depth of mesh will greatly affect capacity. This in turn requires all pumps of a particular type to be built somewhat over capacity in order to insure that the "worst case" pump meets capacity specifications.
A substantial factor resulting in differing capacities in otherwise identical pumps is the fact that conventionally, the bearings are sized to fit the pump chamber. In the usual case, the bearings are manufactured paying close heed to the design dimension between the center of the flat and the diametrically opposite side of the otherwise cylindrical bearing. In order to minimize leakage paths, such bearings are made to relatively tight fit within respective bores in the pump and not infrequently, due to tolerance variations, good fitting cannot always be attained. Thus, it has been customary to, during the assembly process, shave material off of the flats of one or more of the bearings in the hope that a good fit can be achieved. Indeed, the bearings are designed to be shaved so as to accommodate tolerance variation while attempting to maintain a tight fit.
However, in the shaving process, parallelism of the face of the flat to the axial center line of the bearing may be lost, creating a leakage path. Alternatively, the flatness of the face can be lost during the shaving process, again creating a leakage path across the flats. Further, shaving may result in a loss of squareness of the face of the flat to the end of the bearing which in turn may not seal properly against the housing end wall or which may prevent the bearing from moving properly in response to shaft deflection during operation. Most significantly, shaving will result in a changed depth of mesh of the gears journalled by the bearings and accordingly alter the pump's capacity.
The present invention is directed to overcoming one or more of the above problems.